Brønsted Acid Catalyzed Cyclization of Hydroxylated Enynes: A Concise Synthesis of Five‐Membered Heterocycles

Abstract

A mild and direct pathway for the formation of five-membered heterocyclic compounds from hydroxylated enynes has been developed. In this reaction, hydroxylated enynes were selectively transformed into five-membered heterocyclic compounds 2, with an allene moiety at the 3-position, in the presence of F(3) CSO(3) H (0.1 mol %). When R(1) , R(2) =Ph, diphenylvinyl-2,3-dihydro-1H-pyrrole (2 y) was obtained. With HSbF(6) (5 mol %) as the catalyst, polycyclic skeletons 3 and 4 with adjacent stereocenters were obtained. When R(1) =H and R(2) =styrene, 1,3-dienyl-2,5-dihydro-1H-pyrrole (6 as) was formed. This Brønsted acid catalyzed domino process involves the formation of an allene carbocation intermediate, which can be readily trapped by olefins to give various novel five-membered heterocyclic skeletons.

Recent Advances in the Synthesis of Heterocyclics via Cascade Cyclization of Propargylic Alcohols

“…Subsequently, the same group employed a powerful strategy for the construction of fused polycyclic heterocyclic skeletons 57 and 57′ via HSbF 6 ‐catalyzed cascade cyclization of propargylic alcohols 56 bearing two alkenyl groups [31] . This novel transformation proceeded smoothly to provide the corresponding polycyclic skeletons in moderate to high yields under mild conditions (Scheme 20).…”

Recent advances in the cascade reactions of enynols/diynols for the synthesis of carbo- and heterocycles

“…Subsequently, the same group reported a practical and atom-economic transformation to achieve the synthesis of fused polycyclic heterocyclic skeletons 71 and 71′ through the HSbF 6 -catalyzed domino reaction of enynols 70 bearing another alkenyl unit (Scheme 27). 35 In this transformation, a series of structurally complex polycyclic compounds were obtained in good to excellent yields with low regioselectivity under mild conditions. Based on the structures of the obtained products, the reaction mechanism was proposed.…”